1. Field of the Invention
The present invention relates to light sources for optical instruments, and more specifically relates to a light source and a reflectometer employing such a light source for use in a chemical analyzer.
2. Description of the Prior Art
There are many chemical analyzers currently being utilized for automated testing of essentially dry, analytical elements in the form of test slides. The test slides are formed as a multi-layer element containing the necessary reagents for reaction with components of a biological fluid, such as blood serum, deposited thereon. Certain reactions calorimetrically produce a change in optical density which is sensed by a reflectometer of the chemical analyzer, the amount of light reflected from the element varying in accordance with the reaction and being indicative of the amount of a particular component present in the fluid.
One such chemical analyzer having a reflectometer is disclosed in U.S. Pat. No. 5,089,229, entitled “Chemical Analyzer”, which issued on Feb. 18, 1992 to Thomas Heidt, et al., the disclosure of which is incorporated herein by reference. FIGS. 18, 31a, 31b and 31c of the aforementioned Heidt et al. patent illustrate the reflectometer assembly of the analyzer disclosed therein. The reflectometer assembly includes several light sources, including fluorescent lamps or tubes and light emitting diodes (LEDs), each of the light sources emitting a light of different wavelength.
FIG. 1 of the present application corresponds to FIG. 31b of the aforementioned Heidt et al. patent, and illustrates the LED light source assembly 426 disclosed in the Heidt et al. patent. The LED light source assembly basically includes a mounting block 458 situated below a rotatable turntable 50 which carries reagent test slides. The mounting block 458 includes a plurality of spaced apart bores 460 formed through its thickness. Each bore is sloped to the vertical and, preferably, is at an angle of 45 degrees to the vertical. In a preferred form of the invention, four bores 460 are formed spaced equally distantly about the general periphery of the mounting block 458.
Four light emitting diodes (LEDs) 462, each emitting a light of different wavelength, are mounted in the underside of the mounting block 458, each LED 462 being received by a corresponding bore 460. The mounting block 458 is situated with respect to the rotatable turntable 50 such that light emitted by any one of the LEDs will impinge on the bottom of the film portion 124 of a test slide 71 carried by the rotatable turntable 50.
A bore 464 is formed centrally through the mounting block 458. A collimating lens 466 is mounted in the bore 464 and near the top surface of the block 458. A photodiode 468 is also mounted in the bore 464 and near the lower surface of the block 458. Interposed between the lens 466 and the photodiode 468 and in bore 464 is an infrared rejection filter 470.
Light from any LED 462 impinging on the test slide 71 will be reflected directly into the photodiode 468 through the lens 466 and filter 470. The photodiode will provide a signal indicative of the amount of light reflected to the associated circuitry of the reflectometer.
As described in the aforementioned Heidt et al. patent, four LEDs 462 are provided, each LED emitting a light of different wavelength. The preferred wavelengths emitted by the LEDs are in the following ranges: about 555 to about 565 nm; about 585 to about 595 nm; about 635 to about 645 nm; and about 675 to about 685 nm. The aforementioned Heidt et al. patent states that the optimal wavelength for each of the LEDs is 560 nm, 590 nm, 640 nm and 680 nm, respectively. Preferably, the latter two LEDs (i.e., 640 nm and 680 nm LEDs) are disclosed in the aforementioned Heidt et al. patent as having associated therewith filters 469 of the desired wavelength (i.e., 640 and 680 nm) positioned in their respective bores 460.
The aforementioned Heidt et al. patent describes each of the four LEDs 462 as being individually energized so that a single beam of light having a particular wavelength or range of wavelengths will be selected to impinge on a particular test slide.
Various tests to be performed by the chemical analyzer require different test slides, where each test slide carries a different dry analyte. The various test slides must be exposed to light of selected frequencies in order to conduct a reflectometry test. The type of test slide, for example, for a calcium test, is provided by bar code information carried on the test slide, which bar code information is read by a bar code optical scanner of the chemical analyzer and which is provided to the associated computer and circuitry of the analyzer. The computer of the analyzer will energize an appropriate light source, that is, either one of the fluorescent tubes or one of the LEDs, during the analysis operation when a particular test slide 71 is situated in alignment with a particular light source. For a detailed description of how the chemical analyzer uses reflective light to determine the concentration of the chemistry in the serum deposited on the test slide, reference should be had to the aforementioned Heidt et al. patent.
The chemical analyzer with the reflectometer described above of the aforementioned Heidt et al. patent has been successfully commercialized for many years and provides accurate test results. The present invention is directed to an improvement in the reflectometer disclosed in the aforementioned Heidt et al. patent.